1. Field of the Invention
The present invention relates to an adhesive label that has non-adhesiveness at a time of storage and is allowed to exhibit adhesiveness at a time of use.
2. Description of the Related Art
In recent years, adhesive labels have been used for a price indication label, a product indication label, an advertisement label, a seal label for a package, and the like. As a method of recording on a recording surface of the adhesive label, various methods such as an inkjet recording method and a thermosensitive recording method are applied. Conventionally, the adhesive label has a configuration in which an adhesive layer and release paper are laminated on a surface opposite to the recording surface for characters and the like. The release paper is peeled off at a time of use to expose the adhesive layer, and the adhesive label is attached by pressing. However, in the conventional adhesive label to be used by peeling off the release paper, the release paper after being peeled off from the adhesive label completes its function and is disposed of as waste. Therefore, there is a demand for an adhesive label that does not create waste of release paper from the viewpoint of resource protection and environment.
In order to solve the above-mentioned problem, a label that does not use release paper has also been proposed. Specifically, there has been proposed a label in which a thermosensitive adhesive layer that has non-adhesiveness at room temperature and exhibits adhesiveness by heating is formed on a surface opposite to a printed surface of a label. In this label, release paper is not required, and hence, problems related to environment and waste as in the related art do not arise. However, the label in which the thermosensitive adhesive layer is formed is stored by being rolled into a roll shape or by being stacked, and hence, the adhesive surface and the printed surface are stacked on one another in contact. Therefore, in the case of long-term storage or depending upon storage environment, there is a problem of so-called blocking, in which the thermosensitive adhesive exhibits slight adhesiveness, and this causes the printed surface and the adhesive surface to adhere to each other. Further, as heating means for exhibiting adhesiveness by using an adhesive, it is considered to use a heat source such as a thermal head. However, when the thermal head is used for allowing the thermosensitive adhesive layer to exhibit adhesiveness by heating in addition to printing, there arises a problem that power consumption increases.
Japanese Patent Application Laid-open No. 2006-78733 describes an adhesive label that does not use release paper and solves the problems such as blocking. As illustrated in FIG. 7 (FIG. 2 of Japanese Patent Application Laid-open No. 2006-78733), the adhesive label 100 has a laminated structure in which a base 101, an adhesive 102, and a resin film 103 are laminated. A polyester film is used as the resin film 103, and the resin film 103 has a thickness of 1 to 3 μm. The adhesive label 100 prevents blocking at a time of storage by covering the surface of the adhesive 102 with the resin film 103 instead of release paper or a thermosensitive adhesive. Then, at a time of use, a hole is opened in the resin film 103 by using a needle 110, or a stretched polyester film is used as the resin film 103 and a hole is opened in the resin film 103 by heating with a thermal head or the like, to thereby break a blocking prevention function and expose the underlying adhesive 102. In this manner, adhesive strength is exhibited.
Further, Japanese Patent Application Laid-open No. 9-111203 describes a configuration in which a pressure-sensitive adhesive layer is provided on a base sheet, and the pressure-sensitive adhesive layer is covered with a microcapsule layer so as to cover an adhesive surface of the pressure-sensitive adhesive layer, to thereby solve the problems such as blocking without using release paper. The microcapsule layer is formed of a single layer of a hollow microcapsule and has a melting point of about 100° C. to 180° C., for example, and the surface thereof has no adhesiveness. Therefore, release paper is not required. At a time of use, the microcapsule layer is broken by heating with a thermal head to expose the underlying pressure-sensitive adhesive layer, and thus, adhesiveness is exhibited.
Regarding the adhesive label described in Japanese Patent Application Laid-open No. 2006-78733, when labels are issued continuously, the labels are allowed to pass under a state in which the resin films 103 that are adhesive surfaces of the labels are brought into contact with a roller having a needle-shaped surface. With this, a hole is opened in each resin film 103 to expose an adhesive. However, the adhesive adheres to the needle 110 when the hole is opened in the resin film 103, and if the roller is rotated, the resin film 103 is pulled to be broken further. Therefore, the position and area of a region in which adhesiveness is to be exhibited cannot be controlled with high precision. In addition, the adhesive 102 and the resin film 103 scatter and adhere to the roller or the inside of the device, which makes it difficult to keep the transportability of the label. Further, in the case of using a stretched polyester film as the resin film 103 and opening a hole in the resin film 103 by heating with a thermal head, the polyester film in direct contact with a heating part is melted to be opened, and the underlying adhesive functions so as to prevent the opening. The adhesive 102 is originally used for acting on an adherend, but in this case, the adhesive function works strongly with respect to the upper polyester film, which hinders the deformation and flowing of the film in contact. Therefore, it is difficult to stably form an opening in a required shape. When the heat energy at a time of heating is increased, the shape of an opening of the polyester film becomes further unstable, and the underlying adhesive is also heated to break the polyester film and scatter the broken strips thereof, which is not practical.
Further, in Japanese Patent Application Laid-open No. 9-111203, the microcapsule has a spherical shape, and hence, the heat conductivity when the microcapsule comes into contact with a heat source is low. Thus, large heat energy is required for breaking the microcapsule. For this reason, the adhesive label of Japanese Patent Application Laid-open No. 9-111203 is not suitable for a label issuing device of a low power consumption type.